1. Field of the Invention
The present invention relates to artificial teeth for anterior teeth portions which are formed of any one of synthetic resin, ceramics and a composite material of synthetic resin with ceramics, and are of a structure and geometry especially suitable for the preparation of partial dentures or overdentures.
2. Statement of the Prior Art
Partial dentures or overdentures are an intra-oral removable type of prostheses applied to a wide variety of teeth-deficient states from the failure of one tooth to the remaining of one tooth. These dentures are much more frequently used as compared with complete dentures, and are thus said to account for approximately 80% of all the dentures now available. The purpose of such dental prostheses is generally broken down into the following four aspects:
(1) Recovery and Amelioration of Aesthetic Appearance. PA1 (2) Recovery and Amelioration of Masticatory Function. PA1 (3) Recovery and Amelioration of Pronouncing Function. PA1 (4) Retainment and Recovery of Sound Intra-Oral Tissue. PA1 (1) Retainers (clasps, attachments, telescopes, etc.). PA1 (2) Connectors. PA1 (3) Artificial Teeth. PA1 (4) Dental Plates.
In particular, the failure of anterior teeth portions with or without a molar deficiency has relation to not only the recovery and amelioration of masticatory function but the rest of the items as well. The recovery and amelioration of aesthetic appearance, which are of course in touch with the face and the recovery and amelioration of dentition, have an intermediate influence upon the mental and physical aspects of patients and affect seriously the rapid mesial migration of distal teeth into a void space. The anterior teeth play an important role in the recovery and amelioration of pronouncing function, because the amelioration of dental and labiodental sounds or the recovery of dyslalia is achieved by prostheses applied to the failed anterior teeth. Referring to the retainment and recovery of sound intra-oral tissue, it is well known that the failure of teeth and a functional occlusion allow the retroplasia and pathema of intra-oral tissue to go wrong. Thus, the prostheses for failed teeth are also important in view of the prevention of such retroplasia. In view of the foregoing, the partial dentures or overdentures are very important prostheses. Since such prostheses are removable in the oral cavity as mentioned above, it is a requisite for them to comprise the following elements.
Of these elements, the retainers, connectors and dental plates should be designed taking into consideration various factors such as the teeth to be retained, the ridge muscles of mastication, the temporomandibular joint and the patient's interest in the intra-oral cleanness. In the selection and alignment of artificial teeth, they are required to be designed depending upon the state of the remaining teeth or the teeth to be retained, while taking into consideration their size, geometry, color tone, direction, proximal relation, occlusal relation, etc. Numerous studies have been made of such retainers, connectors and dental plates, but never before have any studies been made of the structure and geometry of artificial teeth to be used as the anterior teeth portions of partial dentures. Artificial teeth designed for complete dentures are thus still unavoidably used to this end.
However, the following problems arise when the conventional artificial teeth for anterior teeth portions designed for complete dentures are used as parts of partial dentures or overdentures.
(1) In order to make partial dentures or overdentures, it is required to use artificial teeth in combination with a retainer, a connector and a dental plate (especially a metal plate) and so provide therein a space for receiving them. This inevitably requires to cut off a portion of the basal plane of each artificial tooth. Consequently, not only does it take some time to make partial dentures or overdentures but it is also likely that the configurations of the artificial teeth may deform without recourse to versed skill.
(2) If partial dentures or overdentures are made by cutting off a portion of the basal plane of the conventional artificial teeth for anterior teeth portions designed for complete dentures, it is then impossible to obtain the color tone inherent in the artificial teeth. Besides, the retainer and connector as well as the dental plate (especially a metal plate) are seen through. The reasons are that while the conventional artificial teeth for anterior teeth portions designed for complete dentures comprise a three-layered system of enamel, dentine and cervical layers or two-layered system of enamel and dentile layers, it is likely that the cutting of their basal planes may remove all the dentine and cervical layers or the whole cervical layer and a part of the dentine layer, and if necessary even a part of the enamel layer.
(3) In most cases, the conventional artificial teeth for anterior teeth portions used for complete dentures are designed to be used with dental plates joined thereto, so that their cervical segments are made narrow as viewed in the mesiodistal direction and their major diameters are considerably short. Thus, when used as partial dentures or overdentures, they tend to become aesthetically unnatural because of a gap between the interdental pappilae and trap food tailings or dental plaque therein. A short cervical segment, as viewed in the major-diameterical direction, tends to become unfit for the face and age due to lack of no harmony with the remaining teeth suffering from gingival retraction.